It's a Conn 6M (or a 6M transitional, i.e., becoming a 6M). In my not-so-humble opinion this was the best alto sax ever made. That you got it in playing condition for only $25 is incredible - the bargain of a century.
Your alto has a "New York neck" which was an option provided by the factory for those purchasers who, for whatever reason, didn't like the patented microtuner neck. It is infact a sought-after feature among "collectors" for its rarity - particularly if the protective neck plug has survived intact - as yours has !
The serial number you have quoted dates to 1936, which was fairly early in the 6M production run. As well as a photograph of the serial number area, I'd be interested to see a photograph of the LH little finger table and the RH thumb rest, to work out whether it's a full-blown 6M or whether it has a couple of transitional features which were altered in the final version of the 6M. If the G-sharp key has the pointed end facing the outside, and if the RH thumb rest is adjustable, it is in the last stage of transition to 6M. (These two features were altered in the final 6M iteration, but personally, I prefer the earlier version.)
As for the mouthpiece: keep the one that came with the horn (you can have it opened out by a mouthpiece technician), but also get yourself a modern HR mouthpiece. There are some good stock standard ones - one of the best is the Warburton D which I can highly recommend; it has a slightly fatter sound than the Meyer that many altoists like to use - but there are smaller mouthpiece makers who make an excellent personalised product, such as Phil-Tone and 10Mfan. Just make sure the one you get has a medium-large chamber.
I use Red Java 2.5 reeds myself on my own early 6M. As for tip opening, since you go for .108 on tenor, I'd say .080 or .085 should suit you on alto.
http://www.warburton-usa.com/index....48-d-series-hard-rubber-saxophone-mouthpieces
https://phil-tone.com/alto-gallery
https://10mfan.com/alto/
Congratulations ! And good luck with the mouthpiece search !